In general, this invention relates to a temperature compensation circuit. Specifically, this invention provides for a temperature compensation circuit and method that controls the temperature coefficient of an output signal.
Temperature compensation is often employed in situations where a control signal provided by another semiconductor device or circuit has a particular temperature coefficient and the control signal needs to be converted to a different temperature coefficient. For example, in a typical Radio Frequency (RF) application, a gain control signal is produced by a microprocessor. This gain control signal typically has an undesirable temperature coefficient, in that the gain control curve, e.g. voltage versus decibels, is subject to unwanted anomalies with temperature variation.
Prior art temperature compensation circuits, particularly those found in cellular or cordless phones, are typified by the presence of Metal Oxide Semiconductor Field Effect Transistors (MOSFET) and an operational amplifier connected to a reference voltage for controlling the transfer characteristics of gain control input over temperature. These types of prior art circuits typically use voltage to current converters, where the reference and input voltages have an undesirable temperature coefficient and the reference and output currents have a desired temperature coefficient. One drawback of the prior art temperature compensation circuits is that the transfer characteristic does not produce a sufficiently linear result. Furthermore, the transfer characteristic produces a gain control curve where the minimum voltage is the threshold voltage (VT) of the MOSFET device, not zero. This is undesirable because the full control range is limited due to the threshold voltage. Also, the requirement for the operational amplifier adds complexity and cost to the circuit.
Therefore, a need exists to provide a temperature compensation circuit that produces an approximately linear output signal that is capable of a full range of control.